1. Field of the Invention
The present invention relates to a sealing device for a piston rod of a Stirling engine and in particular to a sealing device for preventing invasion of oil into an operating space in a Stirling engine.
2. Description of the Related Art
As shown in FIG. 2, an expansion piston 2 is reciprocally fitted within an expansion cylinder 1 and an expansion chamber 3 is defined therebetween. The piston 2 is operatively connected, via a rod 4, to an output delivery mechanism (not shown) from which an output of the Stirling engine is obtained in the form of, e.g., rotational torque. Vibration of the rod 4 is prevented by a guide member 5 positioned in an intermediate member 6, thereby enabling unitary movement of the rod 4 with the piston 2 in the axial direction. An intermediate chamber 8 is defined between the member 6 and the piston 2. An oil-scraper seal 7 is secured to the intermediate member 6 in such manner that the seal 7 is in sliding contact with the outer periphery of the rod 4 so as to prevent oil, attached thereon, from invading or flowing into the intermediate chamber 8 upon movement of the rod 4 into the intermediate chamber 8. The oil removed by the seal is received in a space 9 defined between the seal 7 and the member 6 and is returned to the output delivery mechanism via a passage 10 formed in the member 6. The expansion chamber 3 is in fluid communication with a compression chamber (not shown) via a heater 11 to be heated to a high temperature by any suitable means for providing a heat source. A regenerator 12 and cooler 13 are connected between the compression chamber and the expansion chamber 3.
Due to the reciprocal movement of the piston 2 in the vertical direction, a pressure P1 in the intermediate chamber 8 will vary. On the other hand, due to the fact that the space 9 is connected to the output delivery mechanism which has a large volume of space, a pressure P2 in the space 9 will vary over a small range, thereby creating a relationship in which P1 is greater than P2. In view of this relationship, the seal 7 moves in a direction away from the outer periphery of the rod 4 or has decreased contact pressure therewith, thereby permitting flow of oil on the rod 4 into the intermediate chamber 8. Thus, the oil is mixed with the operating fluid and the resulting operating fluid contaminates the heater 11, the regenerator 12 and the cooler 13. In addition, carbonization of the oil may stop up the passages through which the operating fluid passes, thereby decreasing the output power and/or efficiency of the engine.